The main object of this project is the induction of specific unresponsiveness to HLA antigens. There are few examples of tolerance in clinical transplantation not dependent upon continuing administration of immunosuppressive drugs. Recent studies indicate that down-regulation of alloimmune responses ad improved graft survival can occur with only 1 preparative blood transfusion, provided that it comes from a donor partially matched for HLA with the recipient. The main effect is a reduction in donor-specific cytotoxic cell precursor frequency (CTLp). This lab has shown that synthetic allopeptides, representing the hypervariable regions of rat MHC class II beta chains, when given orally prior to immunization with peptides or with intact allogeneic spleen cells, induce a haplotype specific state of hyporesponsiveness, and effect which extends to organ grafting experiments in alloimmunized hosts. We plan to develop in vitro and in vivo human experiments to test the feasibility of tolerization with allopeptides, and to compare the immune state after HLA-directed blood transfusions with the effects of allopeptide administration. The hypothesis is that both approaches provide a unique pathway of immunization involving presentation of allopeptides by self MHC molecules. Synthetic allopeptides will be used to define the responses related to specific epitopes in these patients and in normals. Specifically, CTLp, Thp (helper cell precursors), antibodies, cytokine responses, and suppressor cell activity will be measured. The interaction of antigen-presenting cells (APCs), HLA peptides, and T cell responses will be assessed to compare functional effects of presentation by self vs. donor APCs. The state of immunity in transfused dialysis patients and the ability of HLA peptides to tolerize in vivo will also be assessed. Finally, the bifunctional immunotoxins from Project #2 directed to helper inducer T cell subsets, will be tested in vitro for their potential synergistic effects on tolerance induction prior to initiating clinical trials, which will also depend upon in vivo experiments in rhesus monkeys. (Project #3)